The present invention relates to a hot melt adhesive, and particularly a reactive hot melt adhesive having improved hydrolytic stability.
Hot melt adhesives are a well known class of adhesives. Typically these adhesives are applied in a molten form, cooled to solidify and cured using a crosslinking reaction. Of particular interest are the reactive urethane hot melt adhesives. Such reactive urethane hot melt adhesives, however, have little green strength, and, the substrate or workpiece often must be supported until the adhesive can cure to a crosslinked bond. Such adhesives also tend to be unstable in the presence of water and solvents. Thus, there is a need for a reactive polyurethane hot melt adhesive that has a high initial green strength, and is stable, particularly is hydrolytically stable.
With respect to the reactive urethane hot melt adhesives and such adhesives having high initial green strength, a number of urethane compositions have been proposed. For example, U.S. Pat. No. 3,931,077 to Uchigaki et al. proposes a high viscosity hot melt adhesive composition comprising a reactive urethane prepolymer, a specific ethylene-vinyl acetate theremoplastic polymer and a phenolic or abietic acid type tackifying resin.
U.S. Pat. No. 4,585,819 to Reischle et al. proposes a hot melt adhesive composition comprising an isocyanate prepolymer, a thermoplastic polyurethane or polyester and a low molecular weight synthetic resin such as ketone resins or hydrogenation products of acetophone condensation products.
U.S. Pat. No. 4,808,255 to Markevka et al. proposes a urethane prepolymer which is a reaction product of a polyester polyol and isocyanate composition, a tackifier resin and an ethylene-vinyl monomer thermoplastic copolymer resin.
U.S. Pat. No. 5,558,941 to Stobbie, IV et al. proposes a blend of isocyanate-terminated polyurethane prepolymers consisting of a first crystalline prepolymer based on polyhexamethylene adipate and a second prepolymer based on polytetramethylene ether glycol.
There, however, remains a need for reactive hot melt adhesive having both a high initial green strength and excellent hydrolytic stability.